Devices for controlling oxygen content of blood by controlling breathing parameters such as inspiratory time, peak expiratory end pressure, and expired oxygen delivery to the patient are well known. Details of these various systems will be hereinafter discussed in detail in the description of the prior art. None of the prior art, however, utilizes sensed hemoglobin saturation to concurrently and adaptively control the FiO.sub.2 inspiratory time, and the expiratory end pressure of breathing air from a ventilator supplying pulsed positive pressure breathing air to a patient.